How hard are the rocks or stones? Can you break them with a hammer or even a sledge hammer? Rolling ball mills may not help even with steel ball media trying to grind it up. You may need an industrial rock crusher to do the job.

To break it up initially bag up a few rocks, either in a thick, tough plastic bag or fabric and beat it with a hammer... A plastic bag will keep all of the dust and likely be the simplest manner for collecting it quickly.

If the rock only splinters when hit with a hammer then grinding or filing may be the best way to go...